There is general agreement in the literature that immunoglobulin A (IgA) is the most abundant immunoglobulin Ig isotype. In addition, IgA is the primary Ig found at mucosal surfaces in the form of secretory IgA (sIgA). The protective functions of sIgA are fairly well characterized; however, less is known about serum IgA's defensive capabilities. Despite the high concentration of sIgA at mucosal surfaces, there is little information concerning the interaction of sIgA and the Human Immunodeficiency Virus (HIV). Furthermore, serum IgA's interaction with HIV is not well understood. HIV is the etiologic agent of Acquired Immunodeficiency Syndrome (AIDS). AIDS, a chronic disorder, eventually results in death. The most common route of transmission of HIV is through breaks in the mucosal membrane. Based on current literature, it is not clear what role sIgA or serum IgA plays in defense against HIV. However, whole and glandular saliva from healthy individuals and HIV seropositive (HIV+) subjects have been shown to inhibit HIV in vitro. It is clear whether this inhibition is by antibody-mediation, innate factor complexes, or both. In addition, as HIV+ subjects progress to AIDS, serum IgA levels increase, however, total sIgA levels decrease. The increased total serum IgA levels and decreased total sIgA levels in HIV infection suggest selective abnormalities of IgA regulation due to AIDS. Therefore, the proposed studies are intended to define the nature of sIgA and serum IgA interactions with HIV among HIV+ subjects. Initial studies will compare total IgA levels in whole and glandular saliva to serum IgA levels. The comparison of sIgA to serum IgA, including IgA subclasses (IgA1 and IgA2) of antibodies will be characterized by ELISA, utilizing whole, glandular saliva and serum from HIV+ patients against recombinant gp 120 HIV protein. Antigen specificity of sIgA and serum IgA, in addition to IgG and IgM isotypic responses, will be examined by SDS-PAGE immunoblotting employing laser densitometry. Antibody-mediated neutralization assays will characterize inhibition of HIV utilizing affinity-purified whole and glandular salivary sIgA and serum IgA from HIV+ subjects. These studies will provide valuable information on sIgA and serum IgA immunobiology in HIV infection.